The invention is based on an oil separator for crankcase gases of an internal combustion engine, comprising a preliminary separator, a cyclone separator, a fine separator and, if necessary, a valve device that are provided in a cascade arrangement on a cylinder-head hood of the internal combustion engine.
When an internal combustion engine operates, streams of blowby gas are produced between pistons, piston rings, and cylinder walls and, if applicable, in the region of valve guides. This blowby gas—which enters the crankcase or a camshaft housing, or travels above the cylinder head or is guided there—contains fluid components, primarily fine oil droplets or motor oil components with a low boiling point. Larger oil droplets can also be contained in the crankcase gas or even in the camshaft housing gas that are produced by moving drivetrain parts, i.e., piston, connecting rod, crankshaft or camshaft. This is also referred to as “swirl oil”. In order to remove the blowby gases, a venting of the crankcase—which usually extends over the camshaft housing—is provided. These gas/fluid quantities referred to as crankcase gas and occurring intermittently are separated from the fluid components by means of an oil separator and then typically directed to the intake region of the internal combustion engine. By separating the oil, dirt is prevented from accumulating in the downstream regions, and the emission of hydrocarbons is not increased in an undesired fashion.
In the cyclone separator of the oil separator mentioned hereinabove, the crankcase gas is directed through a helical flow path, where it flows very rapidly. Due to the centrifugal forces produced, the fluid components of the crankcase gas are separated radially outwardly on a wall bordering the helical flow path, and the liquid phase travels downward along the helical path because of its weight. It is understood that the flow rate of the crankcase gas inside the helical flow path depends on the quantity of crankcase gas produced per unit of time and on the flow cross-section of the flow path. The quantity of crankcase gas produced per unit of time depends on the piston displacement of a motor vehicle, among other things. For example, with a diesel engine having a piston displacement of 2 to 2.5 l, quantities of crankcase gas amounting to approximately 65 l/min are produced. With some engines, however, only approximately 50 l/min are directed into the oil separator. The minimum quantity should be considered to be 40 l/min.
This makes it necessary for the cyclone separator and/or the helical flow path to be configured with a different flow cross-section depending on the specific requirements. Until now, it was also necessary to produce and stockpile various oil separators each having different cyclone separators for similar engines with different power output, which is considered to be complicated and cost-intensive.